Transplant tray

ABSTRACT

A transplant tray comprises a number of germination cells, each cell including side walls for holding and retaining a growth medium and seeds or seedlings for germination. Each cell has an opening at the top for retrieval of the growth medium and seedlings for transplanting after germination. The cells are connected to or are integral with one another forming a planar structure. The tray further comprises a skirt connected to or integral with the perimeter of the planar structure. When two trays are stacked the skirts of the two trays are nested within each other thereby enclosing the space between the two trays forming a germination chamber. Vent holes of appropriate sizes are provided in the skirts permitting limited and controlled gas exchange between the germination chamber and the environment to enhance the uniformity of germination conditions within the chamber. The vent holes are not so large as to cause significant loss of moisture to an uncontrolled environment. Stand-offs maintain a desired separation between trays when stacked to prevent undesirable disturbance and scraping off of growth medium and seeds. The skirt is slightly tapered to permit nesting of trays, whether empty or full.

BACKGROUND OF THE INVENTION

This invention relates in general to transplant trays and in particularto a transplant tray which can be used to provide a germination chamber.

Large scale farming operations for crops such as celery, cauliflower,peppers and tomatoes entail the necessity for transplanting millions ofseedlings each year. The seedlings are normally started from seeds in acontrolled environment such as that within a greenhouse. Upon reaching adesired size, the seedlings are transplanted for field growth untilmaturity. Since an extremely large number of seedlings are transplantedand cultivated each year, savings of a fraction of a cent per seed willresult in a substantial increase in the profits of the farmingoperation.

In large scale produce farming, transplant trays are frequently used forseed germination. Typically a transplant tray comprises a number ofindividual cells. The cells are filled to the top with a growth medium(usually a mixture of soil and peat moss). The center of the growthmedium in each cell is then pressed from above to form a depression forreceiving a seed. Seeds are then dropped onto the trays so that thecenter depression in the medium of each cell would receive one seed. Thetrays are then stacked on to a pallet and the pallet of trays is in turntransported by forklifts, trailers or trucks to a greenhouse. Each trayis then laid out in the greenhouse; in modern greenhouses, it is laidout on T-shaped support beams known as T-rails in the greenhouse, but inolder greenhouses, it is simply laid out on benches or on the ground.While in the greenhouse, the seeds germinate and the seedlings growuntil they emerge from the growth medium in a few days.

The seedlings are allowed to grow until they reach a desired size anduntil the growth media in the cells are bound by the roots of theseedlings. The transplant trays are then transported to the field. Theseedlings are transplanted in a manner so that the roots of theseedlings and the growth medium bound by the roots remain intact toreduce transplant shock to the seedlings as is well known in the art.After transplanting, the crops are then cultivated until maturity uponwhich they are harvested.

A transplant tray commonly used in produce farming is in the form of asolid expanded or foamed polystyrene body with holes therein to form thecells, such as that shown in FIG. 1 of U.S. Pat. No. 3,667,159 to Todd.Each cell is generally of squared configuration and tapers downwardlyinto a small opening at the bottom. A conventional tray such as thatproposed by Todd is disadvantageous for a number of reasons. Parts ofthe foamed polystyrene tray may break off particularly at the edges, sothat the cells at the edge of the tray cannot retain as much growthmedium as is necessary for the healthy growth of seedlings and may evencause the roots of seedlings to grow outside the cells. When the traysare stacked onto a pallet and the pallet transported by forklifts,trailers or trucks to the greenhouse, the top part of a tray in thestack is in contact with the bottom part of the tray immediately above.When the trays are filled with growth medium, some cells may beover-filled so that the growth medium and the seeds therein are atelevations above the top of the tray. Thus, when another tray is stackedon top of such tray, the growth media and the seeds above the top of thetray may be scraped off by the tray immediately above in the stackingprocess or in the subsequent transportation. This reduces yield.

When the above-described foamed polystyrene trays are used, the roots ofthe seedlings frequently grow into the polystyrene material forming theside walls of the cells so that when the seedlings are transplanted,parts of the roots may be broken when the seedlings are pulled from thecell, thereby damaging the seedlings. Furthermore, the polystyrene traysare light so that when empty trays are transported by forklifts ortrucks over bumpy roads, the stacks of empty trays are unstable and mayfall off the forklift or truck. A strong wind may also scatter thetrays. The above-described disadvantages have been remedied to someextent by using improved injection molded plastic trays. When theplastic trays are empty, they can be stacked to improve stability duringtransport on bumpy roads; they are also heavier so that they are not aslikely to be scattered by wind. Such plastic trays are availablecommercially from several manufacturers. However, the plastic trays aresimilar to the standard expanded (or foamed) polystyrene trays in that,when such trays are filled with growth media and stacked, the bottomportions of the cells of a tray in the stack are in contact with thegrowth media contained in the tray immediately below when stacked, sothat the growth media and seeds at elevations above the top of the traybelow may again be scrapped off. In the case of some types of plastictrays now available, the bottom portions of cells of a tray may actuallycompress the growth media and seeds in the cells of the tray immediatelybelow. It is therefore desirable to provide trays which do not have suchdisadvantageous when stacked.

As described above, when the seedlings reach a certain stage ofdevelopment, the seedlings together with the growth medium are ready tobe transplanted to a more permanent location for cultivation untilmaturity. Crops such as celery are left in the greenhouse typically for70-80 days before they are transplanted whereas cauliflower is typicallyleft for 30-50 days. During the entire process from germination untilmaturity, it is desirable to provide conditions which will insure thatthe crops mature at about the same time. The resulting uniformity at thetime of harvest increases the percentage of crops which can be harvestedat one time which in turn results in higher yields and/or reducedharvesting cost.

Once the seedlings are transplanted, they are usually in an open fieldwhere the soil, water supply, fertilizer and weather conditions are muchless controllable than when they are in a greenhouse. Therefore toincrease the chances that a batch of crops will mature at the same time,it is important that they germinate and emerge at about the same timewhile they are still in a controlled environment such as in agreenhouse. For this reason, it is important to provide germinationconditions which are uniform for the entire batch of seeds so that theywill emerge from the growth media at about the same time. To provideuniform germination conditions, it is desirable for the transplant traysto be laid out in the greenhouse immediately after seeding so that theenvironment surrounding the trays may be controlled to be uniform.Furthermore, the conditions in the greenhouse may be controlled tooptimize germination. With most crops, this means heating the greenhousewhich is expensive.

In order to save expensive space in the greenhouse, some growers electto keep their seeded trays in a stack for several days in anuncontrolled environment, such as in an open field where the stack oftrays is covered by tarpaulin. When left in an uncontrolled environment,temperature within the stack of filled trays is seldom consistent andoxygen starvation can occur in the middle of the stack. Uneventemperature and humidity within the stack frequently causenon-uniformity in germination and emergence. Thus, when conventionaltransplant trays are used, a grower must choose between letting theseeded trays occupy expensive space in a greenhouse or suffernon-uniform germination and emergence. It is therefore desirable toprovide transplant trays which enhances the uniformity of germinationand emergence when the stack of trays are left in an uncontrolledenvironment.

Different solutions have been proposed for improving uniformity ofgrowth when the stacks of seeded trays are left in an open area. Thus,the stacks may be placed in storage bins to reduce moisture loss and toincrease the uniformity of temperature and humidity uniformity withinthe stacks. This procedure may require many storage bins and much labor.Thus the limited improvement in moisture retention and growth uniformityusing the bins is achieved only at considerable expense. Such solutionis therefore not entirely satisfactory.

In U.S. Pat. No. 3,965,614, Kienholz describes an apparatus forsprouting seeds such as bean sprouts. The apparatus comprises a verticalarrangement of alternately stacked base members and dish members. Thebeans to be sprouted are placed on the dish members which are formedwith a foraminous bottom wall and an upturned peripheral side wall. Eachdish member is then covered by a base member which has an imperforatetop wall with a recessed portion for retaining water. Each dish memberrests on the top wall of a similar base member with water in itsrecessed portion. Thus, the beans to be sprouted in a dish member arekept humid by evaporation from the water retained by the recess in thetop wall of the base member immediately underneath the dish member. Thedownturned side wall of the base member is spaced apart from theupturned side wall of the dish member. Since the radial dimension of thedish member is also less than the radial dimension of the base member, apassageway is formed between the chamber for sprouting seeds and theoutside environment to assure ventilation of fresh air around the beansprouts.

The apparatus proposed by Kienholz described above is apparently notsuitable for transplanting. Transplant techniques usually require thatthe seeds germinate in a growth medium. The roots of the seedlings wouldgrow in the medium so that, when the seedlings together with the growthmedia are transplanted, the seedlings would suffer much less shock ascompared to seedlings whose roots are not surrounded by growth medium.Since Kienholz's dish members are foraminous, they are not suitable forretaining a growth medium. Hence Kienholz's apparatus is not suited fortransplanting.

Furthermore, Kienholz did not provide individual compartments forindividual seeds, so that the roots and seedlings sprouted will becomeentangled thus making transplanting cumbersome and frequentlyimpossible. Since the sprouting chambers between the dish and basemembers are ventilated to the outside environment, water must beprovided in the recess of the base members to insure a humid environmentfor sprouting. The provision of water in a transplanting environment maybe difficult and costly. The apparatus proposed by Kienholz thereforeappears to be disadvantageous for transplanting purposes.

A transplant apparatus is illustrated for example in Canadian Pat. No.1,009,843 to Bergeron et al. Bergeron et al. disclose a seedling traygrowing apparatus comprising a flat support plate having a number ofopenings through it to support a number of cells open at both the topand bottom ends, one cell in each of the openings. Each of the cells isfilled with a growth medium and seeded. The support plate is supportedon a frame with four corner legs. The upper corners of the frame for thesupport plate are recessed into which the corner legs of another supportplate may fit; this allows stacking of support plates. The corner legsare of sufficient length to maintain the bottom of the cells above thesupporting surface. This permits air circulation beneath the cells asrequired for air pruning of roots growing out of the bottom of thecells.

The apparatus disclosed by Bergeron et al. leaves the growth media andthe seedlings in the cells exposed to the environment into which thetrays are placed. When left in an open field, the growth media in thecells may lose moisture so quickly that germination may not occur unlessthey are continually watered. Netherlands Pat. No. 7,406,925 discloses atransplant device which shares the same disadvantages as those explainedabove for Canadian Pat. No. 1,009,843.

In U.S. Pat. No. 3,667,159, Todd discloses a seedling flat formed by anumber of cells joined together, with side walls and end wallssurrounding the cells illustrated in FIGS. 4 and 5. In the patent, Todddid not explain the function of the side and end walls. However, as willbe apparent from FIG. 5, the side and end walls have the same height asthe cells so that no clearance is left between trays when stacked.Hence, the temperature and humidity conditions within the stack may beuneven. The, growth media and seeds left on trays at elevations abovethe tops of the trays may be scraped off. When the trays are filled andstacked, the roots of the seedlings will apparently not be automaticallyair pruned. Moreover, the seedling flats of FIGS. 4 and 5 of Todd cannotbe nested so that a stack of empty flats may be scattered by wind and beunstable in transport over bumpy roads.

SUMMARY OF THE INVENTION

The transplant tray of this invention comprises a plurality ofgermination cells, each cell including side walls for holding andretaining a growth medium and seeds or seedlings therein forgermination. Each cell defines an opening at the top for retrieval ofthe growth medium and seedlings for transplanting after germination. Thecells are connected to or are integral with one another forming a planarstructure, said planar structure having a perimeter. The transplant trayfurther comprises an enclosure means connected to or integral with theperimeter of the structure so that when the structure is stackedvertically with the planar structure of a second transplant tray of thesame type, the space between the two structures will be enclosed by theenclosure means of the two trays to reduce the lost of moisture presentin said space.

Thus, when two transplant trays are stacked, the enclosure means of thetrays enclose the space between the two trays so that the space forms agermination chamber. Loss of moisture in the chamber is reduced. Agrower may therefore leave a stack of trays in an open field with littlefear that the growth media and the seeds or seedlings will dry out.

In the preferred embodiment, the enclosure means is a skirt whichsurrounds the perimeter of the planar structure of the tray. Preferably,the skirt defines therein at least one vent hole to allow limited gasexchange between the germination chamber and the environment into whicha stack of trays is placed. The hole is of such size relative to thesize of the chamber that, when a stack of trays is placed in an openfield, the loss of moisture from the chamber to the environment throughthe hole does not significantly affect germination. The hole is of suchsize that when a stack of trays is placed in a controlled atmosphere,the atmospheric condition in the germination chamber will conform to adesired condition.

According to another aspect of the invention, means are provided tomaintain a separation between trays when stacked, so that after thetrays are filled with a growth medium and seeded, the growth medium andseeds that remain at an elevation above the top of a tray will not bescraped off when the trays are stacked or transported. In the preferredembodiment, the means for maintaining a separation between trays whenstacked are stand-offs extending from the top surface of the planarstructure downwards to a location beneath the bottom of the cells sothat when the trays are stacked, the bottom of the stand-offs of a traywill rest on the top surface of the planar structure of the trayimmediately below to maintain the separation. If the stand-offs arelocated in identical locations of all the trays in the stack, the weightof trays and their contents will be transmitted to the trays belowthrough stand-offs so that the entire weight of the stack will besupported through the stand-offs.

Accordingly to yet another aspect of the invention, the skirt of thetray is slightly tappered vertically so that when the trays are stacked,the skirt of the top tray will be nested within the skirt of the bottomtray to increase the stability of the stack, which is particularlyimportant when the trays are empty and when the stack is transported inwindy weather or over bumpy roads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portion of a transplant tray toillustrate the preferred embodiment of the invention.

FIG. 2 is a top view of a corner of the transplant tray of FIG. 1.

FIG. 3 is a bottom view of a corner of the transplant tray of FIG. 1.

FIG. 4 is a cross-sectional view of a number of transplant trays stackedtogether to illustrate the preferred embodiment of the invention.

FIG. 5 is a partially schematic and partially top view of a system whichincludes transplant trays for providing controlled germinationconditions to illustrate the invention.

FIG. 6 is an enlarged cross-sectional view of a portion of twotransplant trays stacked together within the dotted line 6 of FIG. 4 toillustrate the preferred embodiment of the invention.

FIG. 7 is the cross-sectional view of tray 10' of FIG. 6 taken along theline 7--7 in FIG. 6 to illustrate the preferred embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective cutaway view of one corner of a transplant tray10 viewed at an angle from the bottom of the tray to illustrate thepreferred embodiment of the invention. As shown in FIG. 1, tray 10comprises a number of cells 12 connected together or integral with oneanother to form a planar structure 14. Each of the cells 12 comprisesside walls 22 for holding and retaining a growth medium and seeds orseedlings therein for germination.

FIG. 2 is a top view of a corner of tray 10 to illustrate the preferredembodiment of the invention. As better shown in FIG. 2, each of thecells 12 defines an opening at the top for retrieval of the growthmedium and seedlings (not shown in FIG. 2) for transplanting aftergermination. As shown in FIG. 2, the cells 12 are connected to orintegral with each other by their top portions of their side walls, sothat the top surface of the planar structure 14 is formed by the topsurface of the common side walls of the cells 12, forming a grid-likesurface 24 as shown in FIG. 2. It will be understood, however, thatcells 12 may be connected in a manner different from that illustrated inFIG. 2, and that all such configurations are within the scope of theinvention. At least some of the cells 12 define holes 26 at the bottomfor drainage and for air pruning of roots.

As best shown in FIG. 1, tray 10 comprises a skirt 30 which completelysurrounds the perimeter of the planar structure 14. FIG. 3 is a bottomview of a corner of the transplant tray of FIGS. 1 and 2. FIG. 4 is across-sectional view of a stack of transplant trays of the same type astray 10 illustrated in FIGS. 1-3, where the cross-section of each trayis taken along a line similar to line 4--4 in FIG. 1. As best shown inFIG. 4, when the trays are stacked together as shown in the figure, theskirts of two contiguous trays overlap to enclose the space between thetwo trays. Thus, as shown in FIG. 4, the skirts 30', 30" of trays 10',10" enclose the space 40 between the two trays. Similarly, for thespaces 40 between the trays 10", 10"' and between each pair ofcontiguous trays below, space 40 is enclosed by the two skirts of thecontiguous trays.

As shown in FIGS. 1 and 4, skirts 30, 30', 30", 30"' . . . each definestherein one or more vent holes 42. Vent holes 42 are of such sizerelative to the size of the space 40 that when the stack of trays 50 ofFIG. 4 is placed in an uncontrolled environment, the loss of moisturefrom spaces 40 to the environment through holes 42 does notsignificantly affect germination. Thus, in contrast to conventionaltransplant trays described above, the transplant tray of this inventionencloses the space between trays when stacked to reduce the loss ofmoisture present in the space and preserves such moisture necessary forgermination. As described above in reference to FIG. 4, the space 40between two contiguous trays are enclosed by the skirts of such trays.While in the preferred embodiment as shown in FIG. 4, the trays areprovided with skirts for enclosing the spaces between contiguous trays,it will be understood that other means for enclosing the spaces betweentrays may be used and are within the scope of this invention.

While the loss of moisture from spaces 40 through holes 42 to theenvironment may not significantly affect germination, vent holes 42 dopermit gas exchange through diffusion between spaces 40 and theenvironment surrounding the stack 50. The gas exchange will preventoxygen starvation in the middle of the stack and increase the uniformityof germination conditions throughout the stack. This will enhanceuniformity in germination and emergence. As will become clear below,such gas exchange is further limited by the structure of the tray 10 toreduce the loss of moisture from spaces 40.

The size of the holes 42 is such that when the stack 50 of FIG. 4 isplaced in a controlled environment as illustrated in FIG. 5, theatmospheric condition in the spaces 40 will conform to a desiredcondition for germination. FIG. 5 is a partly schematic and partlybroken away top view of a system for providing the desired germinationconditions. As shown in FIG. 5, one or more stacks of trays 50 are eachplaced on a pallet 60 and the pallets are then placed in a chamber 62enclosed within wall 64. As will be evident from FIG. 5, a large numberof stacks 50 may be placed in chamber 62. The temperature and humiditywithin chamber 62 are controlled by a heater and humidifier 70 whichsupplies warm and humid air to chamber 62. The gas exchange betweenspaces 40 and chamber 62 causes the atmospheric conditions within stacks50 to conform to the desired temperature and humidity conditions forgermination. Since gas exchange occurs through the vent holes 42 betweenall the spaces 40 and chamber 62, the temperature and humidity withineach of the spaces 40 are made to conform to the desired germinationconditions. Hence, substantially uniform temperature and humidityconditions are achieved throughout every portion of the stacks 50.Therefore the seeds will germinate and emerge at about the same time.Since the humidity and temperature within spaces 40 can be controlled bycontrolling the heater and humidifier 70, the germination conditionswithin spaces 40 can be optimized to accelerate the germination process.

An additional feature of tray 10 helps to achieve controlled gasexchange between spaces 40 and the environment. As best shown in FIG. 1,cells 12 are interconnected by webs 80 to strengthen the planarstructure 14. FIG. 6 is a cross-sectional view of a portion of the stack50 of FIG. 4 within the dotted line 6 in FIG. 4. FIG. 7 is across-sectional view of a portion of tray 10' taken along the line 7--7in FIG. 6. To simplify the figure, tray 10" has been left out in FIG. 7.As shown in FIG. 6, webs 80 enclose the space between cell 12' and skirt30' except for an opening 82 near the bottom of cell 12'. Therefore inorder for the warm and humid air supplied by heater and humidifier 70 toreach space 40 between the trays, such air must move through paths suchas that indicated by arrow 84 in FIGS. 6 and 7; that is, such air mustpass through the space enclosed by cell 12', webs 80 and skirt 30',through the opening 82 and then into space 40.

With the appropriate settings for air flow from heater and humidifier70, the atmospheric conditions within spaces 40 in stacks 50 can be madeto conform to the desired conditions within a desired short time periodin a manner described below. As shown in FIG. 4 the skirts of the traysare provided with at least two vent holes one on each side of the tray.A conventional means (not shown) may be provided so that the warm andhumid air is supplied to the stack 50 through the vent holes on one sideof the stack and exits through the vent holes on the other side of thestack along paths such as path 86 in FIG. 4.

The above described structure for confining the gas exchange by means ofwebs 8 adjacent to vent hole 42 is also advantageous when stack 50 isplaced in an uncontrolled environment. When a stack of trays of the typedisclosed in the Canadian patent to Bergeron et al is placed in the openfield, air currents generated by air convection are free to pass throughthe spaces between the trays in the stack so that moisture will be lostfrom the trays. With a stack of trays of the type disclosed herein,substantially no air currents will pass through the spaces betweentrays. Instead, gas exchange will occur substantially only throughdiffusion through vent holes 42. Because of the structure of the tray,in order for moisture to escape from space 40 to the uncontrolledenvironment, the moisture must pass through opening 82 before it canescape through vent hole 42. These factors greatly reduce the rate atwhich moisture will be lost to the environment. The circuitous path forthe gas exchange such as that illustrated by arrows 84 in FIGS. 6 and 7enhances the uniformity of temperature and humidity within space 40 sothat the temperature and humidity in the middle of the tray will notdiffer significantly from those closer to the vent holes.

As described above, the size of the vent holes relative to the space 40should be small enough so that the loss of moisture to an uncontrolledenvironment will not be significant. On the other hand the size of thevent hole 42 should not be too small, thereby permitting adequate gasexchange with a controlled environment to achieve uniform temperatureand humidity conditions within the stack. For such purposes it may bedesirable for the ratio of the combined cross-sectional areas of thevent holes of a tray to the volume of the space between two contiguoustrays when stacked to be substantially in the range of one square inch:10 cubic inches to 1 square inch: 1000 cubic inches. A satisfactoryratio may be about 1 square inch: 250 cubic inches.

In order to maintain a separation between the cells in two contiguoustrays when stacked, stand-offs 90 are provided as shown in FIG. 1. Asshown in FIG. 1, such stand-offs are integral with the webs 80 andextend from the junction point of four cells downwards in the bottomview of the tray in FIG. 3. Webs 80 also serve as support for thestand-offs 90. A comparison of the top and bottom views in FIGS. 2 and 3will indicate that when two trays are stacked stand-offs 90 of the toptray in the stack will rest at intersection points such as points 90'90" of the grid-like top surface 24 of the bottom tray in the stack. Insuch manner, a desired separation is maintained between the planarstructures of two trays when stacked. This separation prevents thebottom portions of cells in a tray from disturbing the growth medium andseeds in a tray immediately below in a stack, and prevents the growthmedium and seeds on the bottom tray at elevations above the top of thebottom tray from being scraped off. A desired separation may be about1/8 inches.

As shown in FIG. 1, cells 12 define holes 26 at the bottom for drainage.Stand-offs 90 preserve a separation between trays so that roots growinginto holes 26 will encounter air in space 40 and will be air pruned.

It is preferably for tray 10 to have a sufficient number of stand-offs90 and for the stand-offs to be of sturdy construction for supportingthe weight of the trays when stacked. Thus, as shown in FIG. 4, theweight of the trays, the growth medium and the seeds in the trays abovea particular tray is transmitted through the stand-offs of such tray tothe stand-offs of the trays below. In such manner the weight of all thetrays, the growth media and seeds in the entire stack is transmittedthrough a string of stand-offs 90 to a supporting surface (not shown inFIG. 4) for the stack.

As best shown in FIG. 4, the skirts of the trays are slightly taperedvertically so that when the trays are stacked the skirt of the top traywill be nested within the skirt of the bottom tray to increase thestability of the stack. As explained above, in produce farmingoperations, empty trays are frequently transported or stored in stacks.When the empty trays of the type described herein are stacked, theskirts allow the trays to be nested to improve the stability of thestack as compared to the standard polystyrene trays. As best shown inFIG. 4, the skirt is of such height that it extends beyond the bottom ofthe cells 12 so that when the tray is placed on a supporting surface(not shown in FIG. 4) of a greenhouse, the supporting surface is incontact with the bottom side of the skirt and the bottoms of such cellsare elevated from the supporting surface to increase the uniformity ofair pruning of roots.

In a particular implementation of the preferred embodiment that may besatisfactory, the base of the skirt is about 121/8 inches by 19 inchesin dimensions, the height of the skirt about 23/4 inches, the cellsabout 21/4 inches deep, the stand-offs about 1/8 inch and the nestingbetween skirts of contiguous trays about 3/8 inch.

From the above, methods for providing controlled environments fromgermination using two or more transplant trays have been described. Bysimply stacking the planar structure of a first tray vertically with aplanar structure of a second tray, the space between the two structuresis enclosed by the skirts of the two trays to reduce the loss ofmoisture in the space. By vertically stacking the trays one on top ofanother and by controlling the atmospheric condition of the environmentsurrounding the stack, the atmospheric conditions in the spaces are thenmade to conform substantially to a desired condition.

From the above, it will be evident that a transplant tray with manyadvantages has been described. When a stack of such trays is placed inan uncontrolled environment, the spaces between the trays areessentially enclosed so that such spaces become germination chambers.The vent holes in the skirts of the trays permit limited gas exchangewith the uncontrolled environment through circuitous paths. Such a slowgas exchange enhances the uniformity of germination conditions withinthe stack without a rapid loss of moisture. When a stack of such traysis placed in a controlled environment, the germination conditions can bemade uniform throughout the stack and can be optimized. Thus, aparticularly advantageous and versatile transplant tray has beendescribed. The stand-offs maintain the desired separation between trayswhen stacked to prevent undesirable disturbance or scraping off ofgrowth medium and seeds. The slightly tapered skirts enable nesting ofempty trays when stacked to improve stability.

The above description of construction and method of the invention aremerely illustrative thereof, and various details and changes in thestructure and steps of the method thereof may be within the scope of theappended claims.

We claim:
 1. A method of providing a controlled environment forgermination using at least two transplant trays, each tray including (a)a plurality of growth cells, each cell including side walls for holdingand retaining a growth medium and seeds therein for germination of theseeds into seedlings and growth of the seedlings, each cell defining anopening at the top for retrieval of the growth medium and seedlings fortransplanting after growth of the seedlings to a predetermined stage,said cells connected to one another to form a planar structure, saidplanar structure having a perimeter; and (b) enclosure means connectedto the perimeter of the structure; said method comprising:putting growthmedium and at least one seed into at least one cell in a first tray; andstacking the planar structure of the first tray underneath the planarstructure of a second tray to enclose the space between the twostructures and the growth medium by means of the enclosure means and theplanar structures of the two trays, to reduce the loss of moisturepresent in said space and in the growth medium, and maintaining aseparation between the planar structures of the two trays, therebypermitting the at least one seed to germinate while the trays arestacked.
 2. A method of providing a controlled environment forgermination using a plurality of transplant trays, each tray including(a) a plurality of growth cells, each cell including side walls forholding and retaining a growth medium and seeds therein for germinationof the seeds into seedlings and growth of the seedlings, each celldefining an opening at the top for retrieval of the growth medium andseedlings for transplanting after growth of the seedlings to apredetermined stage, said cells connected to one another to form aplanar structure, said planar structure having a perimeter; (b) skirtmeans connected to the perimeter of the structure, and (c) traysepartating means for spacing the trays when stacked, wherein the traysare in a controlled environment, wherein when growth medium is placed inat least some of the cells of the trays and the trays are placed in avertical stack, the skirts of two contiguous trays enclose the spacebetween the two trays and the growth medium in the cells in the bottomtray and wherein the skirt of one of the two trays defines a vent holeto allow gas exchange between the space and the enviornment through saidhole; said method comprising:putting growth medium and at least one seedinto at least one cell in a first tray; and vertically stacking thefirst tray underneath a second tray, so that the skirts of the traysenclose the spaces and the growth medium in the at least one cellbetween the trays except for the vent hole which controls gas exchangebetween the spaces and the environment; and controlling the atmosphericcondition of the environment so that the atmospheric condition in thespaces substantially conforms to a desired condition, therby permittingthe at least one seed to germinate in the desired condition while thetrays are stacked.
 3. A transplant tray for providing a germinationenvironment when stacked vertically with a second transplant tray havingthe same structure as that of the tray claimed, said tray comprising:aplurality of growth cells, each cell including side walls for holdingand retaining a growth medium and seeds therein for germination of theseeds into seedlings and growth of the seedlings, each cell defining anopening at the top for retrieval of the growth medium and seedlings fortransplanting after the seedlings have grown to a predetermined stage,said cells connected to one another forming a planar structure, saidplanar structure having a perimeter; and enclosure means connected tothe perimeter of the structure, said structure including stand-off meansso that when the structure is stacked vertically with the planarstructure of the second transplant tray, the cells are spaced apart fromthe planar structure of the second tray, and the space between the twostructures and the growth medium in the cells will be enclosed by theenclosure means and planar structures of the two trays to reduce theloss of moisture present in said space and in the growth medium in thecells.
 4. The tray of claim 1, wherein said enclosure means comprises askirt surrounding the perimeter of the structure.
 5. The tray of claim4, wherein at least some of the cells define holes at the bottom toallow drainage and air pruning of roots of the seedlings in such cells,and wherein said skirt is of such height that when said tray is placedon a supporting surface of a greenhouse, the supporting surface is incontact with the bottom side of the skirt, said skirt including meansfor causing the bottoms of such cells to be elevated from the supportingsurface to increase the uniformity of air pruning of roots.
 6. The trayof claim 4, wherein said skirt is slightly tapered vertically so thatthe tray is stacked with the second tray, the skirt of the top tray willbe nested around the skirt of the bottom tray to increase the stabilityof the stack.
 7. The tray of claim 4, wherein the skirts of the traysenclose the space between the two structures completely, except that atleast one of the skirts defines at least one vent hole therein to allowgas exchange between the space and the exterior of said hole, the holebeing of a predetermined size relative to the space so that when saidtwo trays are stacked and placed in an uncontrolled environment, theloss of moisture from the space to the environment through the hole doesnot significantly affect germination, and so that when said traysstacked and placed in a controlled atmosphere, the atmospheric conditionin the space conforms to a desired condition.
 8. The tray of claim 7,wherein said tray is a unitary structure made by injection molding. 9.The tray of claim 7, wherein the skirt defines at least one pair ofholes, one on each side of the perimeter of the structure, said holesbeing of such sizes that the ratio of their combined cross-sectionalareas to the volume of the space between the trays when stacked issubstantially in the range 1 sq. in.:10 cu. in. to 1 sq. in.:1000 cu.in.
 10. The tray of claim 9, wherein said ratio is about 1 sq. in.:250cu. in.
 11. The tray of claim 3, wherein said stand-off means areconnected to the cells and extending below the planar structure, so thatwhen the tray is stacked vertically with the second tray, the stand-offmeans of the top tray will contact the top surface of the bottom tray tomaintain a separation between the cells in the two trays, therebypreventing the bottoms of the cells in the top tray from disturbing thegrowth medium or seeds in the cells in the bottom tray and from scrapingoff the growth medium and seeds above the cells in the bottom tray. 12.The tray of claim 11, further comprising webs connecting the stand-offmeans to the cells and serving as supports for the stand-off means. 13.The tray of claim 11, wherein the top portions of the side walls of thecells are connected to one another to form the planar structure so thatthe planar structure has a grid-like top surface, and wherein thestand-off means comprises a plurality of stand-offs which are located atsuch locations relative to the cells that when two trays are stacked, atleast some of the stand-offs of the top tray are supported by thegrid-shaped top surface of the planar structure of the bottom tray tosupport the top tray.
 14. The tray of claim 13, wherein the stand-offmeans each extends downwards from a junction point of four contiguouscells, so that when a number of trays are filled with growth media andseeded and then stacked, the weight of the trays and of their contentswill be transmitted through the stand-off means to a supporting surfacefor supporting the stack.
 15. A transplant tray for providing agermination environment when stacked vertically with a second transplanttray having the same structure as that of the tray claimed, said traycomprising:a plurality of growth cells, each cell including side wallsfor holding and retaining a growth medium and seeds therein forgermination of the seeds into seedlings and growth of the seedlings,each cell defining an opening at the top for retrieval of the growthmedium and seedlings for transplanting after growth of the seedlings toa predetermined stage, said cells connected to one another forming aplanar structure, said planar structure having a perimeter; and skirtmeans connected to the perimeter of the structure and wherein said skirtmeans is slightly tapered vertically so that when the tray is stackedwith the second tray, the skirt of the top tray will be nested aroundthe skirt of the bottom tray to increase the stability of the stack, andstand-off means are provided so that when growth medium and seeds areput into the cells of the two trays and the trays are stacked, the trayswill be nested and the cells of the top tray will be spaced apart fromthe planar structure of the bottom tray as well as from the growthmedium and seeds in the cells of the bottom tray, thereby preventingseeds and growth medium in the cells of the bottom tray from beingdisturbed.
 16. The tray of claim 15, wherein at least some of the cellsdefine holes at the bottom to allow drainage and air pruning of roots ofthe seedlings in such cells, and wherein the height of said skirtexceeds those of the cells so that when said tray is placed on asupporting surface of a greenhouse, the supporting surface is in contactwith the bottom side of the skirt and the bottoms of such cells areelevated from the supporting surface to increase the uniformity of airpruning of roots.
 17. A transplant tray for providing a germinationenvironment when stacked vertically with a second transplant tray havingthe same structure as that of the tray claimed, said tray comprising:aplurality of growth cells, each cell including side walls for holdingand retaining a growth medium and seeds therein for germination of theseeds into seedlings, each cell defining an opening at the top forretrieval of the growth medium and seedlings for transplanting aftergrowth of the seedlings to a predetermined stage, said cells connectedto one another forming a planar structure, said planar structure havinga perimeter; separation means connected to the structure so that whenthe structure is stacked vertically with the planar structure of asecond transplant tray, a desired separation is maintained between thetwo structures and between the growth medium in the cells of the bottomtray and the structure of the top tray, thereby preventing the bottomsof the cells in the top tray from disturbing the growth medium or seedsin the cells in the bottom tray and from scraping off the growth mediumand seeds above the cells in the bottom tray; and barrier meanssurrounding the periphery of each transplant tray, said barrier meanshaving means for limiting air circulation between the exterior andinterior of a stack of said transplant trays.
 18. The tray of claim 17,wherein said separation means comprises a plurality of stand-offsconnected to the cells and extending below the planar structure, so thatwhen the tray is stacked on top of the second tray, the stand-offs willcontact the top surface of the second tray to maintain a separationbetween the cells in the two trays.
 19. The tray of claim 18, whereinthe top portions of the side walls of the cells are connected to oneanother to form the planar structure so that the planar structure has agrid-like top surface, and wherein the stand-offs are located at suchlocations relative to the cells that when two trays are stacked, atleast some of the stand-offs of the top tray are supported by thegrid-shaped top surface of the planar structure of the bottom tray tosupport the top tray.
 20. The tray of claim 19, wherein the stand-offseach extends downwards from a junction point of four contiguous cells,so that when a number of trays are filled with growth media and seededand then stacked, the weight of the trays and of their contents will betransmitted through the stand-offs to a supporting surface forsupporting the stack.
 21. The tray of claim 18, wherein said tray is aunitary structure made by injection molding.